Minor planet

A minor planet is an astronomical object that orbits the Sun directly. According to the International Astronomical Union (IAU), these objects are classified as neither planets nor comets. While the eight major planets are massive, minor planets lack the gravity to clear their orbital neighborhood. This means they share their paths through space with many other objects. Today, the IAU prefers the term "small Solar System bodies" (SSSBs) to describe these objects. This category includes both comets and minor planets.

Minor planets are categorized by where they live and how they move. Asteroids are typically found in the inner Solar System. Many reside in the asteroid belt between Mars and Jupiter. Some are near-Earth objects, which have orbits that bring them close to our world. These include Aten, Apollo, and Amor asteroids, which are defined by their specific distances from the Sun. Some asteroids, called trojans, are gravitationally locked to the orbits of larger planets. We have found Earth trojans like 2010 TK7 and 2020 XL5, as well as Mars and Jupiter trojans.

Distant minor planets exist in the outer Solar System. Centaurs live between Jupiter and Neptune, but they have unstable orbits. Trans-Neptunian objects exist at or beyond the orbit of Neptune. Many of these are in the Kuiper belt, a region located about 55 AU from the Sun. Some are called Plutinos because they exist in a 2:3 resonance with Neptune. Other objects, called scattered disc objects, were likely pushed outward by Neptune's gravity. There are also detached objects like Sedna that stay far outside the Kuiper belt.

The history of how we name these objects has changed many times. The first minor planet discovered was Ceres in 1801. At the time, scientists called it a planet, but they later called it an asteroid. The term "minor planet" was not introduced until 1841. For a long time, it was considered a subcategory of a planet. In 2006, the IAU held a major meeting to reclassify these bodies. This meeting moved Pluto and other objects into the new category of dwarf planets. An object is called a dwarf planet if it has enough gravity to reach hydrostatic equilibrium. This means it becomes an ellipsoidal or rounded shape.

Tracking these objects requires massive amounts of data. The Minor Planet Center has documented over 213 million observations. There are 794,832 known minor planets in total. Of these, 633,135 remain unnumbered. Only 541,128 have orbits stable enough to receive a permanent official number. Out of that group, only 21,922 have official names.

As discovery speeds increase, the official numbers have grown into six figures. In 2005, the highest number jumped from 99,947 to 118,161.

The naming process follows a strict three-step sequence. First, a newly discovered object receives a provisional designation. This is a temporary code using the year and a code for the half-month of discovery. Second, once the orbit is confirmed to be accurate, the object is assigned a number. It is then a numbered minor planet. Finally, the discoverer may choose to give it a formal name. However, most objects never reach this third stage. Many are simply left with their numbers or provisional codes due to the sheer volume of new discoveries.

Naming conventions have evolved from ancient myths to modern culture. Early asteroids were named after Greek and Roman mythology. Later, people used names of famous people or literary characters. Some names have even been quite eccentric. For example, 2309 Mr. Spock was named after a discoverer's cat. Other names include 6042 Cheshirecat and 9007 James Bond. There is one important rule: you cannot name a minor planet after its discoverer. This is a different rule than for comets. Astronomers sometimes bypass this by naming objects after each other as a courtesy.